The present invention relates to a method of producing a laminated iron core.
An electric motor is incorporated with a laminated iron core. The laminated iron core comprises a rotor core and a stator core, and both iron cores are composed by laminating iron core pieces punched from metal sheets.
If rotor core pieces and stator core pieces are coaxially punched from the same metal sheets, a producing yield is far heightened, and a space of installing a progressive die means assembly apparatus can be largely reduced. But when punching the rotor core pieces, followed by punching stator core pieces, oral so when punching the stator core pieces, followed by punching the rotor core pieces, difference between external forms of the rotor core pieces and internal forms of the stator core pieces, that is, a gap therebetween is generally narrow, and a problem is present as follows. For example, when punching the external forms of the rotor core pieces, followed by punching the internal forms of the stator core pieces, punched scraps are narrow in width and broken during punching or turned up as floating, and scraps do not drop downward a die and must be twice punched, or scraps are scratched to hurt a progressive die means assembly.
From the viewpoint of heightening rotating precision, it is especially important that the space between the external form of the rotor core and the internal form of the stator core is made small as a stepping motor, namely, that an air gap therebetween is made, e.g., 20 xcexcm or less, but a problem is that the rotor core piece and the stator core piece cannot be punched from the same metal sheet.
As methods of producing laminated iron cores for solving the above problems, an applicant of this invention has proposed JP-A-6-343248, JP-A-6-351196 and JP-A-7-7895. The essentials common among these inventions are present in punching the rotor core pieces from metal sheets and laminating them, roughly punching magnetic pole teeth of the stator core pieces from said metal sheets coaxially with said rotor core pieces, pressing some portions of said magnetic pole teeth to make thickness locally reduced for causing the reduced portions to develop toward the punched side of the rotor core piece, subsequently punching to form small teeth at front tips of the magnetic pole teeth and side faces thereof, punching the external forms of the stator core pieces, and laminating them.
According to them, some portions of the magnetic pole teeth of the roughly punched stator core pieces are urged in the thickness direction to reduce the thickness thereof, and front tips of the magnetic pole teeth develop toward the punching side of the rotor core piece so as to expand a punching margin of the internal side of the stator core piece. Accordingly, when punching out small teeth of the magnetic pole teeth becoming edges of the internal forms of the stator core pieces, the width of scraps is widened and neither broken nor turned up as floating during punching operation. Thus, it is possible to punch and form the rotor core pieces and the stator core pieces from the same metal sheet, thereby to effectively increase the producing yield.
An inventor made further experiments and studies, and found problems involved with techniques. The abovementioned methods comprise punching out the rotor core pieces from metal sheets, roughly punching the magnetic pole teeth of the stator core pieces, and pressing some portions of them to be reduced for developing toward the space sides by previously punching, but difficult is to steadily secure a developing amount or to make an optimum amount. In addition, another problem is that ruggedness formed on a surface of the metal sheet by pressing causes disturbances in a flow of a magnetic flux.
This invention has been realized in view of the above mentioned circumstances, and it is an object of the invention to offer a method of enabling to steadily obtain gaps of high precision for reducing gaps between a rotor and a stator by punching rotor core pieces from metal sheets, roughly punching magnetic pole teeth of stator core pieces, and pressing some portions of them to be reduced.
It is another object of the invention to obtain laminated iron cores having excellent characteristics, in which the magnetic pole teeth of the roughly punched stator core pieces develop toward the space sides made by previously punching the rotor core pieces or make developing of an optimum amount to sufficiently secure the punching margins for pressing the front tips of the magnetic pole teeth becoming the internal forms of the stator core pieces, and the punching can be performed without obstacles even if gaps with the rotor core pieces are small, and further ruggedness formed on a surface of the metal sheet by pressing does not cause disturbances in a flow of magnetic flux.
The essential point of the invention is present in a method of producing a laminated iron core by punching and laminating the stator core pieces and the rotor core pieces, characterized by punching the rotor core pieces from metal sheets and laminating them, roughly punching the magnetic pole teeth of the stator core pieces from said metal sheets already punched of the rotor pieces, changing positions of the magnetic pole teeth and pressing on a plurality of parts thereof and developing them toward the punched sides of the rotor core pieces, subsequently punching to form the front tips of the magnetic pole teeth composing edge parts of the internal forms of the stator core pieces, and punching the external forms of the stator core pieces and laminating them.
Desirably, the pressing on the plurality of parts by changing the positions in the magnetic pole teeth is characterized in that said pressing is carried out by changing pressing timings.
As to another essential point, the pressing effected on the plurality of parts by changing the positions in the magnetic pole teeth is characterized by taking partial charge of slight reduction of thickness in taking partial charge of development toward the punched side of the rotor core piece.
Other characteristics and merits of the invention will be apparent from explanation for embodiments of the invention.